1. Field
This patent specification relates to a charging method capable of charging a plurality of secondary battery packs (herein after refereed to as a battery pack) such as lithium ion batteries. In particular, it relates to an optimal charging apparatus and method for charging spare (backup) battery packs used in an instrument body and mobile instrument, such as a mobile phone, a digital camera, etc.
2. Discussion of the Background
Due to smallness of a power supply capacity of a charging apparatus, a method of attaching and charging a plurality of battery packs one after another in the charging apparatus has been practiced, and many patent applications thereabout has been filed. Even though the term “a battery” is utilized in the below described literature, plural batteries serially arranged are generally used as a battery pack, because the voltage per cell of this type of secondary battery is small.
For example, Japanese Patent Application Laid Open No. 56-110446 discloses a technology for efficiently charging normal batteries by skipping a battery that expresses abnormally lower voltage during charging. Japanese Patent Application Laid Open No. 56-166731 discloses a technology for charging an inert battery in a similar manner to a normal battery by separately and sequentially charging a plurality of batteries one after another, using a charging control mechanism when controlling charging of each battery. Japanese Utility Model Application Publication No. 4-24759 discloses a charging apparatus that charges a plurality of batteries one after another while detecting completion of charging of each battery. Such an apparatus detects attachment, and initializes and proceeds to charge the uncharged batteries when the uncharged battery is attached. Japanese Patent Application Laid Open No. 7-130399 refers to a technology capable of shortening a charging time period by stopping charging when temperature of a battery in the course of being charged exceeds a prescribed level, then charging the next one, and re-starting charging of the former battery when temperature of the next battery exceeds a prescribed level.
According to these former two applications, charging of an additional uncharged battery must be initiated by freshly attaching the uncharged battery after the entire batteries has been charged, because detection of the uncharged battery is impossible if the uncharged battery is newly attached during charging. The charging apparatus of Japanese Utility Model Application Publication No. 4-24759 inconveniently recharges a charged battery which does not require additional charging, because the charging apparatus returns to an initial condition and starts charging again restarting from the first battery when an uncharged battery is attached, even though the uncharged battery is charged. Although a time period for charging the entire batteries is advantageously shortened, the technology of Japanese Patent Application Laid Open No. 7-130399 takes a long time period in completing charging of the first battery in comparison with a case when charging one by one. Further, since an uncharged battery is not detected, charging can be started only by freshly attaching the uncharged battery after charging of the entire batteries has been completed, similar to the technology of Japanese Patent Application Laid Open No. 56-166731 or the like. Further, a conventional charging apparatus itself typically is bulky and costly, because a control circuit for charge control use in the conventional apparatus is entirely built therein.